e tetrazolium (TZ) test is a quick and potentially precise method for estimating seed viability. However, its efficiency depends on adapting the methodology for each species. e objective of this study was to determine the best seed preparation methodology for TZ testing of sunn hemp (Cro -talaria juncea L.) seeds, as well as establish staining patterns for estimating seed viability. Four seed preparation methods were studied for staining: seed coat removal; longitudinal cross-section cut through the embryonic axis without seed coat removal; longitudinal cut in the distal region of the embryo axis, from the thick-end of the seed through the cotyledons; and transversal cut in the distal region of the embryo axis, across the seed width through the cotyledons. Of the preparation methods studied, the most prom ising was seed coat removal. Staining patterns of seeds prepared in this manner could be easily classified into three classes. Class 1 included viable, vigorous seeds, class 2 included viable, non-vigorous seeds, and class 3 included non-viable seeds. erefore, the TZ test with seeds prepared by removing the seed coat is a promising alternative for identifying possible causes of seed viability loss in production systems.